Clutches have been in use in various forms for many years and are readily known in the art. The purpose of a clutch is to selectively engage and disengage a power source output, most commonly a rotating shaft, to a mechanism desired to be driven by the power source. The most commonly known application for a clutch is to interpose the clutch between an automobile engine and a transmission. The most common configuration of a clutch comprises a flywheel coupled to a rotating engine output such as a shaft and a pressure plate axially spaced from the flywheel wherein the pressure plate is movable toward and away from the pressure plate. A driven disk is interposed between the flywheel and pressure plate. The driven disk is rotatably affixed to the transmission and at its outermost radial extremity includes a plurality of facing elements. During operation, when the clutch is engaged, the pressure plate is forced toward the flywheel clamping the driven disk between the pressure plate and the flywheel inducing a frictional force between the pressure plate, flywheel and the respective facing elements. The induced frictional force then causes the engine torque to be transmitted through the clutch to the transmission.
Once sufficient frictional force is produced to hold the driven disk between the pressure plate and the flywheel, the driven disk is accelerated to a rotational speed matching that of the engine. Since engagement of the clutch is controlled by the operator, the clutch is subject to modulation, or variations in the rate of engagement. If the clutch is engaged slowly, a smooth engagement between the engine and transmission is experienced. However, if operator engages the clutch too rapidly, the driven disk can experience an undesirable and noticeable instantaneous acceleration. In order to prevent the instantaneous acceleration a mechanism for damping the undesirable accelleration is incorporated into the clutch. The mechanism generally adopted for providing such damping is to resiliently bias an outer portion of the disk assembly with respect to an inner portion of the disk assembly, thereby permitting a limited rotation of the outer portion with respect to the inner portion. The resilient members are typically a plurality of compression-type coil springs, wherein the ends of the springs engage both the inner and outer portions of the disk assembly. Torque is then transmitted from the inner portion to the outer portion through the plurality of springs. Thus, any undesirable modulation of the clutch manifested as an instantaneous acceleration is absorbed by the plurality of coil springs.
Engine's having a more powerful output or torque require increased spring resistance to provide a desired damping. An efficient means of increasing spring resistance includes placing a smaller spring inside of and coaxially aligned with an outer spring. In this manner the effective spring coefficient can be increased while minimizing the cross-sectional profile of the total spring area. Since the springs are generally held captive in a cavity formed between two spaced apart spring covers, there is often insufficient bearing area at the ends of the spring cavities to support the ends of the smaller diameter inner springs. This is a result of the spring cavities being a full form pocket. The full form has smooth, rounded edges for the spring to rub against during relative motion between the spring and spring cover. However, such a pocket includes ends that do not allow the spring cover to drive the inner one of the coaxial springs. Therefore, in order to provide the desired bearing area against the ends of the inner springs, additional reinforcing plates are affixed to the inner faces of the spring covers. The disk and one or more stack plates are positioned to fill the space between the two reinforcing plates in a manner to permit the desired limited amount of rotation between the disk and stack plates with respect to the inner portion of the disk assembly.
Since the inclusion of the reinforcing plates increases the number of pieces required for the disk plate assembly and the size of the assembly, elimination of the reinforcing plates is desirable to decrease the number of parts, complexity, and time required to assemble the disk assembly.